In recent years, CCDs and CMOS image sensors, which are solid-state image sensing elements for color images, are used in solid-state imaging devices such as video camcorders, digital still cameras and camera-equipped cell phones. These solid-state image sensing elements utilize, in their light-receiving sections, silicon photodiodes that are sensitive to near-infrared ray imperceptible to human eyes. In such solid-state image sensing elements, it is required that spectral luminous efficacy correction be performed so that colors that are natural to human eyes are produced and, therefore, a near-infrared cut filter which selectively transmits or cuts light rays in a specific wavelength range is often used.
As such a near-infrared cut filter, those filters that are produced by a variety of methods have been conventionally used. For example, a filter in which reflection of near-infrared ray is attained by vapor-deposition of a metal such as silver on a transparent base material such as glass and a filter in which a near infrared-absorbing dye is added to a transparent resin such as an acrylic resin or a polycarbonate resin have been put into practice.
However, a near-infrared cut filter in which a metal is vapor-deposited on a glass substrate not only requires a high production cost, but also has a problem in that, as foreign substance, fragments of the glass substrate cause contamination at the time of cutting the filter. Furthermore, the use of an inorganic material as a substrate has limitations in adapting to the recent reductions in size and thickness of solid-state imaging devices.
Meanwhile, JP-A-H6-200113 (Patent Document 1) discloses a near-infrared cut filter in which a transparent resin is used as a substrate and a near infrared-absorbing dye is incorporated into the transparent resin.
However, the near-infrared cut filter according to Patent Document 1 does not necessarily have sufficient near infrared-absorbing capacity.
Further, the present applicant has proposed near-infrared cut filters comprising a norbornene-based resin substrate and a near infrared-reflecting film in JP-A-2005-338395 (Patent Document 2) and JP-A-2011-100084 (Patent Document 3).